FIELD OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to an optical card, and more particularly to an optical card of write-once type having alternative information record regions.
The optical card has a memory capacity larger than a magnetic card by several thousands to several ten thousands times, so that it may be used for various applications for recording bank booking data, maps, personal health data, etc. In usual optical cards, data could not be rewritten and an error rate due to defects on the optical card amounts to about 10.sup.-3 to 10.sup.-4, and therefore an error correction is indispensable. Further, sometimes the error correction could not be performed correctly depending upon magnitude or degree or defects, so that when data could not be recorded correctly in a data record region and the error correction could not be effected, the relevant data has to be recorded again in another data record region. This function is called the alternatively faculty. Usually the data is recorded in a sector of a track, and thus in the present specification, a sector in which data is recorded again is called an alternative sector and a track including such a sector is called an alternative track.
In Japanese Patent Application Laid-open Publication Kokai Sho 63-44,364, there is disclosed a method of effecting the above mentioned alternative faculty by using alternative sectors. In this known method, as illustrated in FIG. 1, in each track there are provided a plurality of data sectors (sector numbers 0 to 59) and a plurality of alternative sectors (sector numbers 60 to 64). When data is not written in a data sector with the error correction, the same data is written in an alternative sector. In this case, the alternative sectors having successively increasing or decreasing sector numbers are used in succession. In FIG. 1, a data sector of sector number 2 is altered by a first alternative sector having sector number 61 and a data sector of sector number 5 is altered by a second alternative sector having sector number 61. In data sectors which have been changed by alternative sectors there are provided marks by means of which these altered data sectors can be distinguished from other non-altered data sectors.
In this known method, in each of the tracks there are always provided the alternative sectors, and thus a user area in the track is limited materially. In the optical disk, since the memory capacity of a track is very large, the user area in the track is not reduced by the provision of the alternative sectors. However, in the optical card having a small size, the memory capacity of one track is about 1 kilo bytes and when the track is divided into a plurality of sectors, there can be provided only four sectors each having the memory capacity of 128 bytes. If one sector is allotted as the alternative sector, only three sectors are used for recording the data. In other words, in this known method, only 75% of the all the memory capacity can be used as the user area and the efficiency of utilization of the record area is very low.
In Japanese Patent Application Laid-open Publication Kokai Sho 61-243,994, there is described another known method for performing the alternative faculty. In this method, as shown in FIG. 2, when a track 3-3 has such a defect that data could not be written correctly in the relevant track, the same data is written again in a next track 3-4 and at the same time a track number "102" of the track 3-3 is written in a corresponding sub-area 13-2 in a directory region 12 together with file name 4 (File A), starting track number 15 ("100") of main data in which said data written in the track 3-3 is included, and total track number 17 ("4") in which the main data has been written.
This known method has the following two problems. Firstly, since the data which could not be written in a desired track due to defects is recorded in a next track, if there are very large defects such as large amounts of dust and damages which extend over two adjacent tracks, the data could not be recorded correctly in the next track. Then the alternative operation is repeated again, so that a recording time is liable to be prolonged. Secondly, in order to perform the alternative faculty even when the number of tracks in which data could not be recorded correctly due to damages and deteriorations of the optical card is increased, it is necessary to share a larger area for the sub-areas 13-1 to 13-4 shown in FIG. 2. Therefore, an area of the main data recording region is reduced accordingly. Particularly, when the track is divided into sectors or an amount of data of a single file is large, an amount of the alternative management information becomes extremely large, so that a large area has to be shared for the directory region 12.
In Japanese Patent Application Laid-open Publication Kokai Sho 63-103,476, there is proposed yet another known method, in which when data could not recorded correctly in a portion of a record medium due to defects on the record medium, the same data is recorded in an alternative portion and at the same time alternative management information denoting the above mentioned portion is recorded in a predetermined region on the record medium. Upon reading the record medium, at first the alternative management information recorded in the predetermined region is read out and an address of a portion to be read out is changed in accordance with the alternative management information.
In this known method, when the record medium is set on a data reading machine, all the data recorded in the alternative track management information is read out first, so that an initial processing time is liable to be longer. In the optical disk, the data transfer rate is high such as on the order of several hundreds kilo bits per second, so that the initial processing time becomes not so long. However, in the optical card, the data transfer rate is very low such as on the order of several kilo bits per second, because the data is read out by reciprocally moving the optical card with respect to an optical head. Therefore, if the number of alternative tracks becomes large, the initial processing operation requires 30 to 60 seconds. This results in a very long access time.